1. Field of the Invention
The present invention relates to a transreflective liquid crystal display (LCD) apparatus and driving method thereof, and more particularly, to a transreflective LCD apparatus with a single cell gap and driving method thereof, wherein low power consumption can be achieved by equalizing electro-optical characteristics in a transmissive region and a reflective region.
2. Description of the Related Art
Development of information technology has been accompanied by growths in both the market for personal communication devices such as cellular phones and the market for computers and televisions. Naturally, the quality of a display apparatus, which is the visual interface between these devices and the user, has become more important. As a result, a flat panel display, such as an LCD, a plasma display panel (PDP) and an organic light emitting diode (OLED), is increasingly used instead of a conventional cathode ray tube (CRT). Of the different types of flat panel displays, the LCD is the most widely used because it provides high-quality images and it can be manufactured in a wide range of sizes.
An LCD apparatus displays video images using light transmittance of liquid crystals. The LCD apparatus uses a light source because the liquid crystals do not emit light themselves. Typically, the LCD apparatus includes an LCD panel for displaying images and a backlight unit positioned at the rear of the LCD panel to provide light to the LCD panel. This type of LCD apparatus, which displays images by using light from the backlight unit, is commonly used. Although the transmissive LCD apparatus is advantageous in that it is possible to achieve high picture quality, power consumption increases due to the use of the backlight unit. Also, the suitability of transmissive LCD apparatus in portable communication devices is less than ideal because of poor visibility in the open air.
In order to overcome such shortcomings of the transmissive LCD apparatus, a study on a reflective LCD apparatus is actively being conducted. Unlike the transmissive LCD apparatus, the reflective LCD apparatus employs ambient light (for example, external illumination or solar light) as a light source. The reflective LCD apparatus can accomplish low power consumption because it does not use the backlight unit. The conventional reflective LCD apparatus, however, has a slow response speed because the transmission of moving pictures is not its system requirements, and its optical characteristics (e.g., contrast, reflectance) deteriorate. Furthermore, because the reflective LCD apparatus uses ambient light as a light source, its characteristics vary according to the position, intensity and color temperature of the light source compared to the transmissive LCD apparatus, thereby lowering its optical characteristics. Particularly, in the night or dark room where an ambient light source is scarcely provided, the reflective LCD apparatus can not act as the display apparatus unless the optical characteristics are optimized.
A transreflective LCD apparatus is a combination of the reflective and transmissive LCD apparatuses that have the advantages of both types of apparatuses. The transreflective LCD apparatus has a reflective region and a transmissive region existing within one sub-pixel. Transreflective LCD apparatuses can be divided into two groups: that that have double cell gaps and those that have single cell gaps.
FIG. 1 illustrates a transreflective LCD apparatus having a double cell gap. In the Figure, a cell gap 2d of transmissive region TA is twice the distance of the cell gap d of a reflective region RA. An optical passing distance of a transmissive light TL, which is emitted from a backlight unit and passes through a transmissive electrode 3 of the transmissive region TA, becomes identical to that of a reflective light RL which is emitted from an ambient light source and reflected by a reflective electrode 5 of the reflective region RA, thereby showing an enhanced transmittance characteristic. However, it is very difficult to control the cell gap d of the reflective region RA during the manufacturing process due to its thinness. As a result, the yield of a transreflective LCD apparatus 1 having double cell gaps is reduced.
In a transreflective LCD apparatus 1 having a single cell gap as illustrated in FIG. 2, a cell gap d of a transmissive region TA is the same as that of a reflective region RA. The transreflective LCD apparatus 1 having a single cell gap operates mostly in a mixed-mode twisted nematic (MTN) mode. In the MTN mode, however, since the optical passing distance of a transmissive light TL, which is emitted from a backlight unit and passes through a transmissive electrode 3 of the transmissive region TA, is different from that of a reflective light RL, which is emitted from an ambient light source and reflected by a reflective electrode 5 of the reflective region RA, it is difficult to identify the optimal design condition of liquid crystals simultaneously satisfying both an optical characteristic in the transmissive region and that in the reflective region. Furthermore, since electro-optical characteristics in the transmissive region TA and in the reflective region RA are different as illustrated in FIG. 3, different gamma voltages should be used with respect to the transmissive electrode and the reflective electrode. The use of different gamma voltages complicates the driving method of the LCD apparatus and reduces a charge time margin. Moreover, as the development of an additional driver integrated circuit (IC) is needed, power consumption increases.